Radio Frequency Identification Devices, Remote Communication Devices, Identification Systems, Communication Methods, and Identification Methods

ABSTRACT

The present invention provides radio frequency identification devices, remote communication devices, identification systems, communication methods, and identification methods. A radio frequency identification device according to one aspect includes a substrate; communication circuitry coupled with the substrate and configured to receive a wireless signal including an identifier, to process the identifier of the wireless signal and to output a control signal responsive to the processing of the identifier; and indication circuitry coupled with the communication circuitry and configured to receive the control signal and to indicate presence of the radio frequency identification device responsive to the control signal. A communication method according to another aspect includes providing a radio frequency identification device; receiving a wireless signal including an identifier within the radio frequency identification device; processing the identifier; generating a control signal after the processing; and indicating presence of the radio frequency identification device using indication circuitry of the radio frequency identification device responsive to the control signal.

TECHNICAL FIELD

This invention relates to radio frequency identification devices, remotecommunication devices, identification systems, communication methods,and identification methods.

BACKGROUND OF THE INVENTION

Wireless communication systems including electronic identificationdevices, such as radio frequency identification devices (RFIDs), areknown in the art. Such devices are typically used for inventorytracking. As large numbers of objects are moved in inventory, productmanufacturing, and merchandising operations, there is a continuouschallenge to accurately monitor the location and flow of objects.Additionally, there is a continuing goal to determine the location ofobjects in an inexpensive and streamlined manner. One way of trackingobjects is with an electronic identification system.

One presently available electronic identification system utilizes amagnetic coupling system. Typically, the devices are entirely passive(have no power supply), which results in a small and portable package.However, such identification systems are only capable of operation overa relatively short range, limited by the size of a magnetic field usedto supply power to the devices and to communicate with the devices.

Another type of wireless communication system is an active wirelesselectronic identification system. Attention is directed towards commonlyassigned U.S. patent application Ser. No. 08/705,043, filed Aug. 29,1996, incorporated herein by reference, and which describes such activesystems in detail.

These systems include integrated circuit devices which include an activetransponder and are intended to be affixed to an object to be monitored.The devices are capable of receiving and processing instructionstransmitted by an interrogator. A device receives the instruction, ifwithin range, then processes the instruction and transmits a response,if appropriate. The interrogation signal and the responsive signal aretypically radio-frequency (RF) signals produced by an RF transmittercircuit. Because active devices have their own power sources, such donot need to be in close proximity to an interrogator or reader toreceive power via magnetic coupling. Therefore, active transponderdevices tend to be more suitable for applications requiring tracking ofa tagged device that may not be in close proximity to an interrogator.For example, active transponder devices tend to be more suitable forinventory control or tracking.

It may be desired to identify one or more particular remotecommunication devices within the plurality of remote communicationdevices of the wireless communication system. For example, it may bedesired to identify the location of a particular package in the field.An exemplary use is to assist with the quick identification of a desiredpackage within numerous objects in inventory. Thus, there exists a needto provide an improved identification system and identification methodof the remote communication devices.

SUMMARY OF THE INVENTION

The present invention provides radio frequency identification devices,remote communication devices, identification systems, communicationmethods, and identification methods.

A remote communication device including a radio frequency identificationdevice according to one aspect of the invention includes substrate andcommunication circuitry coupled with the substrate. The communicationcircuitry is configured to receive a wireless signal including anidentifier, to process the identifier of the wireless signal and tooutput a control signal responsive to the processing of the identifier.Indication circuitry is coupled with the communication circuitry andconfigured to receive the control signal and to indicate presence of theremote communication device responsive to the control signal.

The indication circuitry emits a human perceptible signal, such as avisible signal, in but one configuration to indicate presence of thedesired remote communication device. Devices of the present inventioncan be utilized in exemplary applications to assist with theidentification of one or more desired remote communication devices.Also, such can be utilized to identify one or more desired objectsassociated with the identified remote communication devices in oneexemplary application. Other aspects are provided in the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is an illustrative diagram of an exemplary wireless communicationsystem.

FIG. 2 is a diagrammatic representation of an exemplary forward linkwireless signal outputted from an interrogator of the wirelesscommunication system shown in FIG. 1.

FIG. 3 is an isometric view of an exemplary remote communication deviceof the wireless communication system shown in FIG. 1.

FIG. 4 is a functional block diagram of internal circuitry according toone configuration of the remote communication device.

FIG. 5 is an illustrative representation of exemplary indicationcircuitry of the remote communication device of FIG. 4.

FIG. 6 is a graphical illustration representing exemplary remotecommunication device operations.

FIG. 7 is a graphical illustration showing further details of theillustration of FIG. 6.

FIG. 8 is an illustrative representation of another configuration ofindication circuitry of the remote communication device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a wireless communication system 10 is illustratedin accordance with one embodiment of the invention. Wirelesscommunication system 10 includes an interrogator 12 and at least oneremote communication device 14. Typically, numerous remote communicationdevices 14 are provided within wireless communication system 10 althoughonly two such remote communication devices 14 are illustrated in FIG. 1.The particular number of remote communication devices 14 which are incommunication with interrogator 12 may change over time. Duringexemplary object monitoring operations, more or less remotecommunication devices 14 can be within a communication range of wirelesscommunication system 10 as objects or packages are moved about.

A communication range 11 of interrogator 12 is shown in FIG. 1.Interrogator 12 communicates with remote communication devices 14located within communication range 11. Typically, there is nocommunication between multiple remote communication devices 14. Instead,remote communication devices 14 respectively communicate withinterrogator 12. As previously mentioned, multiple remote communicationdevices 14 are typically used in the same field of interrogator 12(i.e., within communications range 11 of interrogator 12).

It may be beneficial to determine communication range 11 of interrogator12 in a given application. As described below, one aspect of thedisclosure provides a remote communication device 14 having indicationcircuitry (one configuration is shown in FIG. 3) configured to assistwith the determination of communication range 11 during testingoperations. Such a remote configuration device 14 can comprise a deviceutilized for normal communication or testing operations, oralternatively, for testing operations only.

During testing operations, remote communication device 14 having theindication circuitry of FIG. 3 can be moved throughout an area largerthan and including communication range 11 to assist with thedetermination of communication range 11. Interrogator 12 can be utilizedto output plural forward link wireless signals 22 during testingoperations. Remote communication device 14 operates to output a humanperceptible signal (e.g., human visible light) as described below whenit is present within communication range 11 and receiving forward linkwireless signals 22. Such human perceptible signals can be used toassist with determining communication range 11 of interrogator 12 bynoting where such human perceptible signals are generated as remotecommunication device 14 is moved.

In addition, remote communication device 14 can be utilized to verifycorrect installation and operation of 10 wireless communication system.Remote communication device 14 indicates proper operation andinstallation of interrogator 12 responsive to receiving forward linkwireless signals 22.

In the described embodiment, wireless communication system 10 isconfigured as an electronic identification system. Other configurationsof wireless communication system 10 are possible. Remote communicationdevices 14 can individually be associated with respective objects 16,such as packages in inventory. Wireless communication system 10 can alsobe used in other applications including other identificationapplications.

Remote communication devices 14 individually comprise a wirelessidentification device in the described arrangement. Other configurationsof remote communication devices 14 are possible. An exemplary wirelessidentification device is a radio frequency identification device (RFID).In the depicted configuration, remote communication devices 14individually include an antenna 18 for wireless or radio frequencytransmission by the respective remote communication device 14. Remotecommunication devices 14 further individually include an antenna 20 forwireless or radio frequency reception by the respective remotecommunication device 14. In one embodiment, the antennas 18, 20 aremicrostrip antennas.

Individual remote communication devices 14 transmit and receive radiofrequency communications to and from interrogator 12. An exemplaryinterrogator is described in commonly assigned U.S. patent applicationSer. No. 08/907,689, filed Aug. 8, 1997 and incorporated herein byreference. Preferably, interrogator 12 includes an antenna 13 as well asdedicated transmitting and receiving circuitry. In one embodiment, suchcircuitry is complementary to that implemented within individual remotecommunication devices 14.

Radio frequency identification has emerged as a viable system fortagging or labeling small to large quantities of objects 16. In thedescribed configuration, interrogator 12 and remote communicationdevices 14 communicate via an electromagnetic link, such as via an RFlink (e.g., at microwave frequencies, in one embodiment), so alltransmissions by interrogator 12 are heard simultaneously by all remotecommunication devices 14 within communication range 11.

Interrogator 12 transmits forward link wireless signals 22 individuallycomprising an interrogation signal or command via antenna 13. Referringto FIG. 2, an exemplary forward link wireless signal 22 is shown. Thedepicted forward link wireless signal 22 includes a preamble 23, barkercode 25, tag identifier (ID) 26, command 27, data 28 and check sum 29.

Tag identifier 26 can comprise an identifier to identify one or more ofremote communication devices 14 in some applications. For example, tagidentifier 26 can identify one, more than one, or all of remotecommunication devices 14. As described below, typically only the remotecommunication devices 14 identified within tag identifier 26 process therespective command 27 and data 28.

Referring again to FIG. 1, remote communication devices 14 within theappropriate communication range 11 individually receive the incominginterrogation forward link wireless signal 22 via respective antennas20. Upon receiving wireless signal 22, individual ones of remotecommunication devices 14 can respond by generating and transmitting aresponsive signal or return link communication signal 24 via respectiveantenna 18. The responsive signal 24 typically includes information thata uniquely identifies, or labels the particular remote communicationdevice 14 that is transmitting. Such may operate to identify arespective object 16 with which the responding remote communicationdevice 14 is associated. Exemplary objects 16 include packages ininventory, people, automobiles, animals, etc.

Referring to FIG. 3, remote communication device 14 can be included inany appropriate packaging or housing 30. Various methods ofmanufacturing housings are described in commonly assigned U.S. patentapplication Ser. No. 08/800,037, filed Feb. 13, 1997, and incorporatedherein by reference. An exemplary housing 30 includes an ultrasonicallywelded plastic injection molded case. Housing 30 is provided about asubstrate 31 and at least some of the circuitry of remote communicationdevice 14. Housing 30 can be configured as a case about substrate 31 toenclose most if not all of the internal components of remotecommunication device 14. More specifically, circuitry of remotecommunication device 14 is provided upon substrate 31 in one embodiment.An exemplary substrate 31 is FR4 board. Circuit components of remotecommunication device 14 may be attached to substrate 31 usingpick-and-place processing techniques.

FIG. 3 shows but one embodiment of remote communication device 14 in theform of a card or badge including housing 30 of plastic or othersuitable material. In one embodiment, a face of housing 30 has visualidentification features such as graphics, text, information found onidentification or credit cards, etc. (not shown). Housing 30 can also beformed as a miniature housing encasing the internal circuitry and powersupply 16 to define a tag which can be supported by object 16 (e.g.,hung from an object, affixed to an object, etc.). Other forms ofhousings 30 are employed in alternative embodiments.

In the illustrated embodiment, remote communication device 14 includescommunication circuitry 32, a power source 34 and indication circuitry36. Communication circuitry 32 is defined by a small outline integratedcircuit (SOIC) as described in the above-incorporated patent applicationSer. No. 08/705,043, filed Aug. 29, 1996. Exemplary communicationcircuitry 32 is available from Micron Communications Inc., 3176 S.Denver Way, Boise, Id. 83705 under the trademark Microstamp Engine™ andhaving designations MSEM256X10SG, MT59RC256R1FG-5. Other embodiments ofcommunication circuitry 32 are possible. Power source 34 is connected tosupply power to communication circuitry 32 and indication circuitry 36.

In one embodiment, power source 34 comprises one or more batteries.Individual batteries can take any suitable form. Preferably, the batterytype will be selected depending on weight, size, and life requirementsfor a particular application. In one embodiment, a suitable battery is athin profile button-type cell forming a small and thin energy cell morecommonly utilized in watches and small electronic devices requiring athin profile. A conventional button-type cell has a pair of electrodes,an anode formed by one face and a cathode formed by an opposite face. Inan alternative embodiment, power source 34 comprises a series connectedpair of button type cells. In alternatives embodiments, other types ofsuitable power source are employed. Suitable batteries of power source34 individually include a 3 Volt battery having designation CR2016available from Eveready Battery Co. Two such batteries can be coupled inseries for a 6 Volt output of power source 34 in one embodiment.

In the described arrangement, communication circuitry 32 is coupled withsubstrate 31 and is configured to at least one of receive wirelesssignals and communicate wireless signals. Exemplary received andcommunicated wireless signals comprise radio frequency signals aspreviously described. In one embodiment, communication circuitry 32comprises transponder circuitry configured to output the reply or returnlink wireless identification signal responsive to the reception of aforward link wireless interrogation signal generated within interrogator12.

Indication circuitry 36 is coupled with substrate 31 and communicationcircuitry 32. In the described embodiment, indication circuitry 36includes an indicator 38 to indicate operation of remote communicationdevice 14. Remote communication device 14 can be configured such thatindication circuitry 36 indicates at least one of reception of wirelesssignals and generation of wireless signals. Indication circuitry 36 mayalso be configured to indicate the outputting of wireless signals fromremote communication device 14.

Remote communication device 12 having indication circuitry 36 can alsobe configured to provide additional indication operations in addition tothose described herein. Exemplary additional indication operations ofremote communication device 12 are described in a commonly assigned U.S.patent application entitled “Radio Frequency Identification Devices,Wireless Communication Systems, Communication Methods, Methods ofForming a Radio Frequency Identification Device, Methods of TestingWireless Communication Operations, and Methods of Determining, aCommunication Range”, naming Mark T. Van Horn, David K. Ovard and ScottT. Trosper as inventors, filed the same day as the present application,having attorney docket number MI40-187, and incorporated herein byreference, and in a commonly assigned U.S. patent application entitled“Radio Frequency Identification Devices, Remote Communication Devices,Wireless Communication Systems, and Methods of Indicating Operation”,naming Scott T. Trosper as inventor filed the same day as the presentapplication, having attorney docket number MI40-218, and incorporatedherein by reference.

Indication circuitry 36 includes indicator 38 configured to emit a humanperceptible signal to indicate operation of the remote communicationdevice 14 in accordance with a preferred configuration. In the describedembodiment, indicator 38 is configured to visually indicate operation ofremote communication device 14. In particular, indicator 38 can includeat least one light emitting device, such as a light emitting diode(LED), to emit a signal visually perceptible to humans. An exemplary LEDhas designation L20265-ND and is available from Digi-Key Corp.Indication circuitry 36 can also include other indicators 38 forindicating operation of remote communication device 14. Anotherexemplary indicator 38 includes an audible device, such as a buzzer.Indicator 38 can have other configurations.

Preferably, remote communication device 14 is configured such thatindicator 38 of indication circuitry 36 outwardly emits the humanperceptible signal or otherwise indicates operation outside of housing30. For example, indicator 38 may extend through housing 30 as shown andis externally visible. In the depicted arrangement, housing 30 isprovided about substrate 31 and internal circuitry with indicationcircuitry 36 at least partially outwardly exposed as illustrated.

Referring to FIG. 4, communication circuitry 32 of remote communicationdevice 14 implemented as a single die in accordance with the describedembodiment includes a transmitter 40, a receiver 42, a memory 44, and amicroprocessor 46. Microprocessor 46 is coupled to transmitter 40,receiver 42, and memory 44 as described in U.S. patent application Ser.No. 08/705,043. In one configuration, transmitter 40 is configured toreply using backscatter communications.

Forward link wireless signals 22 are received within antenna 20 andapplied to receiver 42. The forward link wireless signals 22 can bespecific to individual remote communication devices 14, or intended toapply to some or all remote communication devices 14 withincommunication range 11.

Microprocessor 46 is configured to process the signals received byreceiver 42. Responsive to the content of a received forward linkwireless signal 22, microprocessor 46 can formulate return link wirelesssignal 24 which is applied to transmitter 40. Transmitter 40 operates tooutput return link wireless signals 24 using antenna 18. As ispreviously described, transmitter 40 may be configured for backscattercommunications. For example, antenna 18 can be configure dipole antennaand transmitter 40 can selectively short halves of the dipole antennaconfiguration to selectively reflect a continuous wave signal generatedby interrogator 12.

Referring to FIG. 5, operations of communication circuitry 32 andindication circuitry 36 are described. As previously mentioned,communication circuitry 32 can be implemented in a SOIC configuration.The SOIC includes plural pin connections, some of which are illustratedin FIG. 5. For example, a pin 4 is coupled with an internal currentsource (not shown) which is configured to output a current signalcorresponding to backscatter communications. The current signaloutputted from pin 4 corresponds to the control signal utilized tocontrol modulation of the continuous wave signal during backscattercommunications.

Plural pins 5, 6 of communication circuitry 32 can be coupled withantenna 18. In one embodiment, pins 5, 6 can be coupled with respectivehalves of the dipole antenna configuration to implement backscattercommunications. Internal of communication circuitry 32, a switch (notshown) selectively shorts pins 5, 6 to implement the appropriatebackscatter modulation communications. A pin 13 of communicationcircuitry 32 is a ground voltage reference pin.

In the depicted arrangement, pins 4, 13 are coupled with indicationcircuitry 36. The depicted indication circuitry 36 includes indicator38, transistor 50, resistor 52 and capacitor 54 arranged as illustrated.In an exemplary configuration, capacitor 54 is a 0.1 μF 5 mT capacitorhaving designation ZVN3306FCT-ND available from Digi-Key Corp. andresistor 52 is a 620 Ohm ⅛th Watt 5 mT resistor having designationP620ETR-ND available from Digi-Key Corp. Transistor 50 is aZVN3306FCT-ND N-Channel MOSFET transistor available from Digi-Key Corp.

During operations, remote communication device 14 including indicationcircuitry 36 can be moved within an area including communication range11. Interrogator 12 can be provided in a mode to continually transmit anidentify command which prompts a return message from all remotecommunication devices 14 within communication range 11. In such a testmode, remote communication device 14 having indication circuitry 36configured as shown can assist with the determination of communicationrange 11.

For example, following the receipt and processing by microprocessor 46of forward link wireless signal 22 having an appropriate tag identifier26 and identify command 27, remote communication device 14 formulates areturn link wireless signal. Microprocessor 46 formulates the returnlink wireless signal and transmitter 40 is configured to output thereturn link wireless signal. Such return link wireless signals can beapplied via pin 4 to indication circuitry 36. During testing operationsto determine communication range 11, wireless communications via antenna18 can remain enabled or, alternatively, be disabled if return linkcommunication signals are undesired.

Transmitter 40 outputs a current signal via pin 4 to indicationcircuitry 36 during a return link communication. Pin 4 can be coupledwith the gate (G) of transistor 50. Responsive to the gate receivingcurrent from pin 4, the drain (D) connection is coupled with the source(S) connection of transistor 50. Such closes the circuitry withinindication circuitry 36 and illuminates indicator 38 comprising a lightemitting device. A typical backscatter reply signal is 20 ms in thedescribed embodiment. Such results in a visible flashing of indicator 38in the described embodiment corresponding to received forward linkwireless signals 22.

Accordingly, the indication of operations of remote communication device14 using indicator 38 is responsive to processing of the forward linkwireless signal and generation of the return link wireless signal. Otherconfigurations for controlling indicator 38 are possible. Further, theduration of the return link wireless signal can be adjusted in otherconfigurations to vary the length of the indicating signal usingindication circuitry 36.

Referring to FIG. 6, a graph illustrates an exemplary testing operationusing a remote communication device 14 having indication circuitry 36 todetermine communication range 11 of interrogator 12 in one application.Time progresses from left to right in the graph of FIG. 6. A voltageacross resistor 52 of indication circuitry 36 is represented in thevertical direction.

Remote communication device 14 can be moved throughout an area adjacentwireless communication system 10. During such movements, remotecommunication device 14 may be moved in and out of communication range11. Such results in the reception of only, some of the forward linkwireless signals 22 being continually generated using interrogator 12during testing operations. Accordingly, the generation of return linkwireless signals 24 corresponds to received forward link wirelesssignals 22 while remote communication device 14 is moved withincommunication range 11.

The generation of a return link wireless signal 24 results in a spike60. The divisions of the illustrated graph are approximately 250 ms andindividual spikes 60 are approximately 20 ms in length corresponding tothe duration of return link wireless signals 24. The generation of thereturn link wireless signals 24 depends upon the movement of the remotecommunication device 14 with respect to communication range 11. Spikes60 correspond to remote communication device 14 being withincommunication range 11. As illustrated, indicator 38 only generates someemissions responsive to continuous generation of forward link wirelesssignals 22 from interrogator 12 and responsive to remote communicationdevice 14 being moved in and out of communication range 11. Inasmuch asspikes 60 correspond to the emission of light from indicator 38, suchcan be utilized by an individual to visually determine the boundaries ofcommunication range 11 of interrogator 12 in a given application. Thenumber of spikes 60 (i.e., outputted as flashes of light from indicator38 in the described configuration) increases with increasing fieldstrength.

Referring to FIG. 7, one spike 60 is illustrated in detail. Again, timeincreases in the illustrated graph of FIG. 7 from left to right. Thevoltage across resistor 52 of indication circuitry 36 is indicated inthe vertical direction. Some modulation upon the top portion of spike 60results due to backscatter modulation of the signal outputted from pin 4of communication circuitry 32. However, the capacitive effect of thegate pin of transistor 50 minimizes such modulation effects upon theoperation of indication circuitry 36.

Referring to FIG. 8, an alternative configuration of indicationcircuitry 36 a of remote communication device 14 is illustrated. Thedepicted indication circuitry 36 a is coupled with communicationcircuitry 32 and power source 34. Indication circuitry 36 a can beutilized alone or in combination with indication circuitry 36 describedwith reference to FIG. 5 above.

Indication circuitry 36 a is coupled with a data port 35 and a clockoutput 37 of communication circuitry. Port 35 and clock output 37 canrespectively comprise pins 17, 18 of the integrated circuitry comprisingcommunication circuitry 32. Port 35 can comprise a digital port andclock output 37 can comprise a digital clock output. The depictedindication circuitry 36 a includes a latch 70, transistor 50, indicator38, resistor 52 and capacitor 54.

Indication circuitry 36 a provides benefits in numerous applications,such as inventory monitoring as an exemplary application. In particular,assuming there are a plurality of objects 16 which are being monitored,remote communication device 14 containing indication circuitry 36 a canbe utilized to identify one of more desired specific objects from theremaining objects within inventory.

For example, referring again to FIG. 2, a user can input a desiredidentifier within tag identifier 26 of forward link wireless signal 22.The identifier can correspond to a desired object 16 associated with theremote communication device 14 identified by tag identifier 26. Tagidentifier 26 can identify one or more desired remote communicationdevices 14 to identify one or more objects 16.

Interrogator 12 communicates the forward link wireless signal 22 havingthe proper identifier 26 within communication range 11. Remotecommunication devices 14 within communication range 11 receive theforward link wireless signal 22 including identifier 26. Individualremote communication devices 14 receiving forward link wireless signal22 process the received forward link wireless signal 22. Individualremote communication devices 14 identified by the tag identifier 26proceed to process command 27. Other remote communication devices 14 notidentified by tag identifier 26 discard the received forward linkwireless signal 22.

Command 27 within forward link wireless signal 22 can include a commandto write to port 35 of communication circuitry 32. Following processingof command 27, communication circuitry 32 can generate and output acontrol signal to indication circuitry 36 a. Indication circuitry 36 ais configured to receive the control signal and to indicate presence ofthe respective remote communication device 14 responsive to the controlsignal.

In one configuration, communication circuitry 32 is configured to outputa control signal to indication circuitry 36 a comprising data 28 of areceived forward link wireless signal 22. More specifically, command 27can specify the writing of data 28 contained within received forwardlink wireless signal 22 to port 35 of communication circuitry 32. Data28 can comprise a byte for controlling indication circuitry 36 a. Forexample, data 28 can include hex FF to turn on indicator 38. Thereafter,interrogator 12 can communicate another forward link wireless signal 22including hex 00 within data 28. Writing of the hex 00 to data port 35can be utilized to turn off indicator 38. Other data 28 can be suppliedwithin a forward link wireless signal 22. For example, hex AA can beutilized to flash indicator 38.

Data port 35 is coupled with a D-input of latch 70. Communicationcircuitry 32 is configured to output a timing signal to a clock (CLK)input of latch 70 via clock output 37. Latch 70 is configured to receivethe control signal including data 28 from communication circuitry 32.Latch 70 is configured to store data 28 received from communicationcircuitry 32. Further, latch 70 is configured to selectively assert anoutput signal via the Q-output responsive to the received control signalin the described embodiment. The Q-output is coupled with gate (G)electrode of transistor 50. The source (S) electrode of transistor 50 iscoupled with ground and the drain (D) electrode of transistor 50 iscoupled with indicator 38.

Indicator 38 is selectively coupled with latch 70 via transistor 50 andis configured to output a signal to indicate the presence of therespective remote communication device 14 responsive to the controlsignal (e.g., data 28) received within latch 70 from communicationcircuitry 32. As described above, indicator 38 is preferably configuredto emit a human perceptible signal to indicate the presence of therespective remote communication device 14. In the depicted embodiment,indicator 38 comprises a light emitting device such as a light, emittingdiode (LED) configured to visually indicate the presence of therespective remote communication device 14.

In accordance with the presently described embodiment, only the remotecommunication devices 14 identified by identifier 26 of forward linkwireless signal 22 indicate the presence of the respective remotecommunicate devices 14 using indication circuitry 36 a. Accordingly,such operates to identify desired objects from other objects accordingto one application.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-50. (canceled)
 51. A method of tracking inventory, the methodcomprising: placing one or more items at a first location, the one ormore items having a radio frequency identification (RFID) tag attachedthereto; providing one or more interrogators identifying informationassociated with the RFID tag; broadcasting by the one or moreinterrogators a first message, the first message comprising a tagidentifier; receiving by a plurality of RFID tags the first message;communicating by a first RFID tag of the plurality of RFID tags a secondmessage, the first RFID tag being identified by the tag identifier, thefirst RFID tag having a first location; receiving by the one or moreinterrogators the second message; and providing an indication of thefirst location.
 52. The method of claim 51, wherein the indicationincludes a visual indication of the first location.
 53. The method ofclaim 52, wherein the visual indication includes a light.
 54. The methodof claim 51, wherein the indication is provided on the RFID tag.
 55. Themethod of claim 51, wherein the communicating includes backscatteringthe second message.